The field of hydrocarbon production is directed to retrieving hydrocarbon fluids from where they are trapped in subterranean formations. Oil (or gas) wells are drilled into reservoirs where hydrocarbon fluids permeate the rock formations. Hydrocarbons flow from surrounding formations into the well and up the well bore to the surface. An important consideration to hydrocarbon production companies is the production rate, i.e., the rate at which hydrocarbons can flow into the well.
Many formations have low porosity and/or a tight matrix, making it difficult for fluids to pass through the formation to reach a low pressure area (e.g., the immediate proximity of a well). In such formations, the presence of open cracks (or “fractures”) plays an important role in allowing fluids to reach a well. In many cases the reservoirs are naturally fractured, and wells can be drilled into highly fractured areas to maximize the production rate. In other cases, the fractures may be artificially generated from existing wells. In any event, it is desirable to characterize the extent and orientation of fractures in hydrocarbon reservoirs to optimize the location of future wells.
It is important to determine the extent and amount (i.e., intensity) and the orientation (i.e., azimuth) of open formation fractures in order to properly “engineer” the production of hydrocarbons from the field during both primary and secondary recovery periods. (Open formation fractures are those fractures containing brine or hydrocarbons.) In the primary recovery period, the azimuth and the intensity of the open fractures are vital considerations in properly locating and spacing production wells to maximize the production of the hydrocarbons from the fractured formation. In the secondary recovery period, the arrangement of fractures around certain wells is a vital consideration in properly injecting a drive fluid (e.g., water, gas, etc.) into the formation to force hydrocarbon flow towards one or more production wells. If an open fracture connects an injection well directly to a production well, the drive fluids will merely flow through the fracture and bypass most of remaining hydrocarbons.
Thus, it would be desirable to have a reservoir fracture characterization method that accurately identifies and quantifies in a useful way the intensity and azimuth of open fracturing throughout a subsurface formation.